… so the checksum error message is not necessarily given because of the checksum, it could be a problem with a path or else.
In your screenshot the flashing script can’t change the directory (cd) to the images subdirectory. Could be a permissions issue.
The manual installation guide states
" On GNU/Linux , open a terminal emulator, navigate to the archive content directory and execute the script with the command sh flash-for-unix.sh"
Try to run the command in a terminal window with “sudo” before it …
sudo sh flash-for-unix.sh.